John Campbell, a physicist at the University of Canterbury, responded.

Some butterfly and moth wings are brightly coloured to advertise to predators
that they taste terrible. Some tasty ones mimic the colours of the revolting
tasting ones so fewer get eaten by predators. Some are coloured to camouflage
themselves when resting on bark.

Hence the colours of moth and butterfly wings have evolved for many different
purposes. In the same way, the methods by which these colours are produced are
also varied. Some use chemistry, molecules that absorb some visible colours
but not others. When white light falls on a red butterfly wing we see it as red
because the green and blue light has been absorbed but the red is reflected.

When light falls on an array of straight lines it is
diffracted. You can see this by looking at a distant street light through net
curtains. You also see it on reflecting stickers which have areas of bright light
whose colour changes as you rotate the sticker. These stickers are made from
reflecting plastic film which has been stamped with straight lines very close
together.

The wings of the morpho moth are covered with very tiny scales. These are covered
by parallel ridges which are all equally spaced with about 2000 lines in each
millimetre. Morpho moth wings were often included in victorian
paintings because of their brilliantly iridescent blue colour.